Chairs and sofas are typically constructed from posterior and lumbar supporting assemblies having generally a frame with a plurality of springs, a cushion or pad which rests on the springs, and an upholstery cover. These assemblies, although flexible due to their spring construction, assume a predetermined fixed shape which requires that for maximum comfort, persons using such furniture must adjust their body positions relative to these assemblies.
There are many ergonomic supports in the nature of chairs, sofas and the like which include flexible and resilient supporting portions which conform to the body to provide comfort. All of these posterior and lumbar supporting sitting surfaces, whether contoured or non-planar, have the ability to form a plurality of cantilevers which automatically adjust and conform to human body movement without mechanical parts, as opposed to adjusting the human body to conform to the supporting portion of the seating surface.
It is now understood that gluteal spreading, commonly known as “secretary spread” is as injurious to the pelvis and spine as incorrect posture. No matter how comfortable an ergonomic seating device is, continuous sitting on anthropometrically measured seating devices will in most humans result in repetitive stress injuries to the back. U.S. Pat. No. 5,887,951 provides a seating device having a uniform thickness member providing support for a user's pelvic area.